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American Mineralogist; October; v. 93; no. 10; p. 1545-1549; DOI: 10.2138/am.2008.2943
© 2008 Mineralogical Society of America
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Herderite from Mogok, Myanmar, and comparison with hydroxyl-herderite from Ehrenfriedersdorf, Germany

George E. Harlow1,* and Frank C. Hawthorne2

1 Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York 10024-5192, U.S.A.
2 Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada

Correspondence: * E-mail: gharlow{at}amnh.org

The crystal structures of herderite, CaBePO4[F0.75(OH)0.25], a = 9.7446(4), b = 7.6769(3), c = 4.7633(2) Å, β = 90.667(1)°, V = 356.31(4) Å3, P21/a, and Z = 4, from the Mogok Stone Tract, Myanmar, and hydroxyl-herderite, CaBePO4[(OH)0.52F0.48], a = 9.7615(4), b = 7.6680(3), c = 4.7853(2) Å, β = 90.184(1)°, V = 358.18(4) Å3, P21/a, and Z = 4, from the Sauberg mine, Morgenröther Zug, Ehrenfriedersdorf, Germany, have been refined to R1 indices of 1.7%, in both cases, using MoK{alpha} single-crystal X-ray diffraction data. Herderite from Mogok is associated with complex rare-element beryl-type granite pegmatite. Most herderite-series minerals are the product of late-stage processes in granite pegmatite evolution, typically of an exsolved fluid upon crystallization, and significant F-enrichment in these fluids appears to result in the domination of herderite over hydroxyl-herderite. Herderite is now documented from Mogok, Myanmar; Yichung, China; Brazil; and probably Erongo, Namibia. The pegmatites at Ehrenfriedersdorf, Germany have produced samples at the boundary between herderite and hydroxyl-herderite, if not possibly herderite as well.

Key Words: Herderite • hydroxyl-herderite • crystal structure • Mogok • Myanmar • Ehrenfriedersdorf • Germany






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